A Global Positioning System (GPS) is a space based global navigation satellite system that utilizes a network of geo-synchronous satellites that can be utilized by a GPS receiver to determine its location. Many telematics systems incorporate a Global Positioning System (GPS) receiver, which can be used to obtain the location of a vehicle at a certain measured time. Using the signals received by the GPS receiver, the heading information of the vehicle can be determined. A GPS receiver can determine velocity information in a variety of ways including, but not limited to, measuring the Doppler shift of the received signals and by comparing the location of a vehicle at a plurality of measured times. The acceleration of the vehicle can be determined as the change in speed divided by the time between the measurements. A GPS receiver's ability to determine acceleration can be limited due to the dependence of the measurement upon factors such as, but not limited to, reception and satellite availability. In addition to location information, a GPS receiver can also be configured to provide time data. However, measurements determined via a GPS receiver can contain errors that affect the accuracy of the measured information. In particular, GPS signals are vulnerable to signal delays, inconsistencies of atmospheric conditions that affect the speed of the GPS signals as they pass through the Earth's atmosphere, and multipath distortions. Additionally, other factors not listed above can influence GPS signals and result in measurement errors.
An accelerometer is a device that measures acceleration associated with the weight experienced by a test mass in the frame of reference of the accelerometer device. The acceleration measured by an accelerometer is therefore a weight per unit of test mass, or g-force. Thereby, a stationary accelerometer in a vehicle would experience the earth's gravity while a free falling one would not.